Neutralized regenerative amplifier



Dec. 9, 1952 c. A. HULTBERG NEUTRALIZED REGENERATIVE AMPLIFIER Filed Aug. 8. 1945 33 w 1^ a C@ Mn a 0 r 7 x m L wJ NKDN. n

Patented Dec. 9, )1952 NEUTRALIZED REGENERATIVE AMPLIFIER Carl A. Hultberg, Buffalo, N. Y., assignor, by

mesne assignments, to Sylvania Electric Products Inc., New York, N. Y., a corporation of Massachusetts Application August 8, 1945, Serial No. 609,589

6 Claims.

This invention relates to regenerative circuits, and more particularly to regenerative circuits as applied to a pentode tube in a novel manner so as to obtain the benefits of regeneration without its drawbacks.

It is an object of this invention to provide a radio frequency amplifier utilizing a pentode in which the benefits of regeneration are obtained, while drawbacks are reduced.

It is a further object of this invention to provide various forms of regenerative radio frequency circuits applied to a pentodc tube, in which the regeneration takes place between the anode and the suppressor grid.

It is a further object of this invention to provide a regenerative radio frequency amplier employing a pentode in Which the regenerative action takes place between the anode and the suppressor grid while a neutralizing voltage is applied to the screen grid to prevent the undesired effects of regeneration from appearing in the input circuit.

Still other` objects and advantages of my invention will be apparent from the speciiication.

The features of novelty which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its fundamental principles and as to its particular embodiments, will best be understood by reference to the specification and accompanying drawing, in which Fig. 1 is a circuit diagram of a typical pentode amplier, showing the circuit elements, to which consideration is given, and from which the operating conditions desired may be better understood,

Fig. 2 is one form of improved circuit in accordance with this invention,

Fig. 3 is a somewhat modified form, and

Fig. 4 is a still further modified form.

In the various gures, like reference numerals indicate like parts.

Referring now more particularly to Fig. l, a typical pentode may comprise cathode Ille, control electrode Ig, screen electrode Isc, suppressor electrode Illsr, and anode Ita. The input circuit may be connected between the control electrode and cathode, and control voltage EI is impressed thereon.

Various significant capacities usually inherent in the construction of the tube and the wiring attached thereto are indicated, such as CI, the control grid-cathode capacity; C2, the capacity between screen Isc and control grid Illy; capacity C3 between suppressor Iilsrand control electrode IUg; and capacity C4 between anode Ia and control electrode Ig.

For purposes of analysis, with the tube in' operating condition, various voltages exist between the various electrodes and the cathode, among which may be E2, the voltage from screen Isc to cathode I0; voltage E3 from suppressor Isr to cathode Ille; and voltage E4 from anode Ia to cathode Ic.

In accordance with my invention, regeneration is employed in a pentode by coupling the anode circuit to the suppressor circuit, and a voltage of proper magnitude and phase may also be applied between screen sc and cathode Ic, so that the admittance of the control grid-cathode circuit is substantially the same as if no voltage were present on suppressor I0sr or anode Illa. In other words, viewed from the input terminals, the input circuit of the tube has the same constants as if no regeneration were employed, whereas ordinarily the application of regeneration to a tube results in an effective reduction of the impedance and/or resistance of the input circuit. This may adversely aiect the operation of preceding circuits.

This condition, in which regeneration is applied from the anode to the suppressor circuit While a voltage is applied to the screen to prevent undesired regenerative effects in the input circuit, I terrn neutralization. I am aware that this term has previously been used to describe triode arrangements in which various forms of reverse feedback have been employed to prevent or control undesired oscillation, but the term as used herein has a diierent meaning, as given above.

Referring now more particularly to Fig. 2, in which I have shown the application of the principles of my invention to one form of pentode circuit, the pentode contains the same elements as shown in Fig. l. Cathode Illc may be connected to ground through resistance II shunted by bypass condenser I2. The anode may be connected to a tuned circuit made up of inductance I3 and variable condenser I4, and the B supply obtained through source of plate potential I5, the negative terminal of which may be grounded.

The radio frequency voltage developed in y tuned circuit I3-I4 may be applied to suppressor Isr through condenser I6, which may be also connected through resistance I'I to ground. Screen IEIsc may be coupled through inductance I9 to inductance I3, and connected through suitable source of potential I8 to ground, thus main- 3 taining it at a positive potential with respect to cathode. The input voltage may be impressed between control electrode and ground, and the output voltage taken between anode and ground at the output terminals.

If the output circuit contains a load, the A. C. plate voltage can be completely expressed as E4=(M-I-7N)El in terms of the input voltage. For constant regeneration, E3=KE4 for neutralization as above dened. Voltage E2 may be impressed on the screen, and this will be a fraction of E4; for instance, E2=WE4- Then the input admittance is Y=5iw[C1-|-{1+W(M+7'N)}C2+ Let Yo equal the admittance when E2, E3, and E4 are zero.

For the purposes of this discussion, A. C. values only need be considered. W may have any -I- or -f value, and in some cases may even be zero. The optimum value of W is obtained by equating Yo to Y of Equation 1.

N -l tan M is common 'to all terms, we can simplify and obtain In order for perfect neutralization to take place, the voltage sources for E2 and E3 voltages should have negligible impedance to the current. In general 'this condition may be closely approached by the circuit shown in Fig. 2. Since C2 is many times larger than C3 and C4, W will in general be much smaller than K. If this were not true, then W would be so large that it would cause the net plate circuit feedback to be degenerative rather than regenerative.

Referring now more particularly to Fig. 3, in this instance the plate voltage may be obtained by the connection of the plate source to one side of tuned circuit I3I4 rather than to an intermediate point on inductance I3 as in Fig. 2, and condenser I6 may be connected to one terminal of inductance I9 instead of to inductance I3. Screen source I8 may be connected to an intermediate point on winding I9. Otherwise the circuit is substantially the same as that shown in Fig. 2, and no further description is believed to be necessary.

Referring now more particularly to Fig. 4, I have shown still a further modication, in which resistance Il and condenser IS may be omitted. In this instance the plate circuit arrangement is the same as that of Fig. 3, :but screen Iiisc may now be connected through winding I9, as in Fig. 2, winding I9 being coupled to inductance I3 and connected through source I8 to ground.

An additional winding 2 I may be provided, connected at one end vto suppressor Iesr and through an additional source of biasing potential to ground, or directly to ground through contact 23. Switch -22 may be employed if desired, to permit connection o f suppressor I'Bsr either directly to ground or to ground through source 2).

In any case, however, it will be observed that the circuits of Figs. 2, 3, and 4 operate to apply a regenerative voltage to suppressor |831' from the plate circuit, and that they also apply to screen I0sc neutralizing Voltage which prevents the input circuit of the tube being aected by the regenerative action, thus making it possible to utilize the benefits 0f increased gain and selectivity obtainable from regeneration without the reduction of resistance or impedance of the input circuit, which might interfere with or reduce the eiciency of circuits feeding the input circuit.

In the speciiication I have explained the principles of my invention and the best mode in which I have contemplated applying those principles, so as to distinguish my invention from other inventions; and I have particularly pointed out and distinctly claimed the part, improvement, or combination which I claim as my invention or discovery.

While I have shown and described certain pre- `ferred embodiments of my invention, it will be understood that modifications and changes may be made without departing from the spirit and scope thereof, as will be clear to those skilled in the art.

I claim:

l. The combination with a vacuum tube having a cathode, an anode, and at least three grid electrodes between cathode and anode, of a tuned circuit connected between cathode and anode, means for impressing a voltage derived from said tuned circuit between cathode and the grid electrode nearest the anode to produce regeneration, means for impressing a Voltage of different phase between cathode and the next successive electrode nearest the anode to neutralize in the cathodecontrol electrode circuit the regenerative eects of the rst voltage, and an input circuit connected between cathode and the third grid.

2. The combination with a vacuum 'tube having a cathode, an anode, a control electrode, a screen electrode, and a suppressor electrode, of a tuned circuit connected between cathode and anode, means for impressing a voltage derived rom said tuned circuit between said Cathode and said suppressor electrode to produce regeneration, means for impressing a second voltage of diiTerent phase between said cathode andY said screen electrode to neutralize in the cathodecontrol electrode circuit the effects of regeneration, and an input circuit connected between cathode and the control electrode.

3. The combination with a vacuum tube having a cathode, an anode, a control electrode, a screen electrode, and a suppressor electrode, of a tuned circuit connected between anode and cathode, a first inductance coupled thereto and connected between the suppressor and cathode to apply to said suppressor electrode a Voltage of opposite phase to that at said anode, a second inductance coupled thereto and connected between the screen electrode and cathode, the voltages of said last two mentioned inductances being of substantially opposing phase to neutralize in the cathode-control electrode circuit the regenerative eiects of said inst-mentioned voltage, and an input circuit connected between said cathode and said control electrode.

Li, The combination with a vacuum tube having a cathode, an anode, a control electrode, a screen electrode, and a suppressor electrode, of a tuned circuit including an inductance connected between cathode and anode, a connection from an intermediate point on said inductance to the cathode, a connection from one end of said inductance to the suppressor electrode, said connection including a capacity, a second inductance coupled to the rst inductance and connected between the screen electrode and cathode and an input circuit connected between cathode and the control electrode.

5. The combination with a vacuum tube having a cathode, an anode, a control electrode, a screen electrode, and a suppressor electrode, of a tuned circuit connected between anode and cathode, said tuned circuit including an inductance, a second inductance coupled to said first inductance, said second inductance having its opposite terminals connected to the screen and suppressor electrodes with the screen-electrode terminal of the same polarity as the anode terminal of said iirst-mentloned inductance to neutralize in the cathode-control electrode circuit the regenerative effect of the voltage applied v the voltages impressed between suppressor and cathode and screen and cathode are out of phase to neutralize in the cathode-control electrode circuit the regenerative effect of the voltage supplied to said suppressor electrode, and an input circuit connected between said cathode and said control electrode.

CARL A. HULTBERG.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,230,483 Cage Feb. 4, 1941 2,312,139 Weagant Feb. 23, 1943 2,315,043 Boucke Mar. 30, 1943 

